// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
#define CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_

#include <memory>
#include <string>

#include "base/memory/ref_counted.h"
#include "base/sequenced_task_runner_helpers.h"
#include "content/browser/webui/url_data_manager.h"
#include "content/common/content_export.h"
#include "ui/base/template_expressions.h"

namespace base {
class RefCountedMemory;
}

namespace content {
class URLDataManagerBackend;
class URLDataSource;
class URLDataSourceImpl;

// Trait used to handle deleting a URLDataSource. Deletion happens on the UI
// thread.
//
// Implementation note: the normal shutdown sequence is for the UI loop to
// stop pumping events then the IO loop and thread are stopped. When the
// URLDataSources are no longer referenced (which happens when IO thread stops)
// they get added to the UI message loop for deletion. But because the UI loop
// has stopped by the time this happens the URLDataSources would be leaked.
//
// To make sure URLDataSources are properly deleted URLDataManager manages
// deletion of the URLDataSources.  When a URLDataSource is no longer referenced
// it is added to |data_sources_| and a task is posted to the UI thread to
// handle the actual deletion. During shutdown |DeleteDataSources| is invoked so
// that all pending URLDataSources are properly deleted.
struct DeleteURLDataSource {
    static void Destruct(const URLDataSourceImpl* data_source)
    {
        URLDataManager::DeleteDataSource(data_source);
    }
};

// A URLDataSource is an object that can answer requests for data
// asynchronously. URLDataSources are collectively owned with refcounting smart
// pointers and should never be deleted on the IO thread, since their calls
// are handled almost always on the UI thread and there's a possibility of a
// data race.  The |DeleteDataSource| trait above is used to enforce this.
class URLDataSourceImpl : public base::RefCountedThreadSafe<
                              URLDataSourceImpl, DeleteURLDataSource> {
public:
    // See source_name_ below for docs on that parameter. Takes ownership of
    // |source|.
    URLDataSourceImpl(const std::string& source_name,
        URLDataSource* source);

    // Report that a request has resulted in the data |bytes|.
    // If the request can't be satisfied, pass NULL for |bytes| to indicate
    // the request is over.
    virtual void SendResponse(int request_id,
        scoped_refptr<base::RefCountedMemory> bytes);

    const std::string& source_name() const { return source_name_; }
    URLDataSource* source() const { return source_.get(); }

    virtual bool IsWebUIDataSourceImpl() const;

    // Replacements for i18n or null if no replacements are desired.
    virtual const ui::TemplateReplacements* GetReplacements() const;

protected:
    virtual ~URLDataSourceImpl();

private:
    friend class URLDataManager;
    friend class URLDataManagerBackend;
    friend class base::DeleteHelper<URLDataSourceImpl>;

    // SendResponse invokes this on the IO thread. Notifies the backend to
    // handle the actual work of sending the data.
    virtual void SendResponseOnIOThread(
        int request_id,
        scoped_refptr<base::RefCountedMemory> bytes);

    // The name of this source.
    // E.g., for favicons, this could be "favicon", which results in paths for
    // specific resources like "favicon/34" getting sent to this source.
    const std::string source_name_;

    // This field is set and maintained by URLDataManagerBackend. It is set when
    // the DataSource is added, and unset if the DataSource is removed. A
    // DataSource can be removed in two ways: the URLDataManagerBackend is
    // deleted, or another DataSource is registered with the same name. backend_
    // should only be accessed on the IO thread. This reference can't be via a
    // scoped_refptr else there would be a cycle between the backend and data
    // source.
    URLDataManagerBackend* backend_;

    std::unique_ptr<URLDataSource> source_;
};

} // namespace content

#endif // CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
